This invention relates generally to improvements in water purification systems of the type having a reverse osmosis unit or the like for removing dissolved ionic material and other contaminants from an ordinary supply of tap or feed water. More particularly, this invention relates to a reliable purity or water quality monitor for incorporation into a water purification system, wherein the monitor is responsive to cyclic operation of the reverse osmosis unit to accurately determine and indicate the operational efficiency of the reverse osmosis unit.
Water purification systems in general are well-known in the art of the type having a reverse osmosis unit for converting an incoming supply of ordinary tap or feed water into relatively purified water for use in cooking, drinking, etc. In general terms, the reverse osmosis unit includes a semi-permeable membrane through which a portion of the tap water supply is passed, such that the membrane acts essentially as a filter to remove dissolved metallic ions and the like as well as undesired particulate matter from the tap water. In operation, these impurities are removed from one portion of the water flow and concentrated in another portion of the flow which is normally discharged as waste to a drain. The thus-produced supply of relatively purified water is normally passed into a temporary storage reservoir or vessel where it is ready for dispensing and use, typically by operation of an appropriate faucet valve located adjacent a kitchen sink or the like. While the specific construction and operation of the purified water supply system may vary, such systems are exemplified by those shown and described in U.S. Pat. Nos. 4,585,554; 4,595,497; 4,657,674; and 5,045,197.
In many instances, it is desirable to obtain an indication of the degree of purity of the purified water produced by the reverse osmosis unit. Alternately stated, it is desirable to obtain an indication of the operating efficiency of the semi-permeable membrane within the reverse osmosis unit. In this regard, the level of water purity will depend upon and thus will vary in accordance with several factors, such as the cleanliness of the reverse osmosis unit membrane and the degree of contamination of the incoming tap water supply in a raw state. The purity level of produced purified water is normally indicated by a measurement of electrical conductivity, wherein a relatively high electrical conductivity correlates with a relatively low resistance and thus reflects a substantial quantity of remaining ionic material which has not been removed by the reverse osmosis unit. Conversely, a relatively low conductivity level indicates that a high proportion of ionic material as well as other contaminants have been removed. A failure of the purified water to meet certain purification criteria indicates that the water supply system may not be operating properly or otherwise that the semi-permeable membrane may need to be cleaned or changed.
In the past, test devices and systems have been proposed for use in measuring the conductivity level of the produced purified water in a typical purification system. In some cases, the conductivity of the produced purified water has been compared with the conductivity of the incoming tap water, thereby indicating the operational efficiency of the reverse osmosis unit in proportion to the condition of the tap water inflow. In general terms, such test devices and systems have utilized one or more electrodes for contacting the purified water and, in many designs, for contacting the incoming feed water, to obtain the desired water conductivity readings. These electrodes are coupled to an appropriate operating circuit and source of electrical power to obtain the desired purity level readings which can be indicated, for example, by illumination of one or more indicator lights.
Prior water quality monitor test devices have commonly comprised self-contained portable units intended for use by service personnel in testing purified water, as described, for example, in U.S. Pat. No. 3,990,066. More recently, reverse osmosis purification systems designed for under-the-counter use in a typical residence or office environment have been equipped with monitoring circuits integrated directly into the purification system, as shown, for example, in U.S. Pat. Nos. 4,623,451; 4,806,912; 3,838,774; 4,708,791; 5,057,212; and 5,145,575. Indicator lights in such test devices commonly include a red or yellow light energized when the quality of the produced purified water is unacceptable, and a green light energized when the conductivity reading or readings reflect acceptable water quality.
While these test devices beneficially provide important information regarding the performance of the reverse osmosis unit, cyclic operation of a typical reverse osmosis unit often results in erroneous test readings. More specifically, many reverse osmosis systems utilize an inlet shut-off valve which responds to the pressure of the produced purified water to turn off the tap water inflow when the storage reservoir reaches a substantially filled condition. The inlet shut-off valve beneficially stops water flow through the system when the reservoir is full, thereby preventing continuous wasted water flow to the drain. However, during the time that the inlet shut-off valve is closed, the pressure differential across the reverse osmosis membrane, necessary for production of purified water, is substantially removed. As a result, some migration or leaching of contaminants across the reverse osmosis membrane can occur, to increase the impurity level of small or isolated volumes of previously produced purified water resident within system flow paths between the membrane and the storage reservoir. Those flow paths provide a convenient mounting site for a pure water electrode, whereby a high and unacceptable conductivity reading can occur if a measurement is taken when the electrode is in contact with one of these isolated volumes of poor quality water. When system water flows resume upon dispensing of a sufficient portion of the purified water via a faucet valve or the like to re-open the inlet shut-off valve, any isolated volume or volumes of poor quality water mix quickly with other purified water so that the overall quality of the water actually dispensed is quite acceptable. However, many test devices respond to faucet valve opening to immediately take a conductivity measurement, whereby the reading can be inaccurate if the inlet shut-off valve has been closed for an extended period of time. Other test devices operate by taking conductivity readings at set time intervals, whereby an inaccurate reading can occur if taken when the inlet shut-off valve is closed or shortly after opening thereof.
There exists, therefore, a significant need for further improvements in water quality monitors for testing and indicating the operating performance of a reverse osmosis unit in a water purification system, particularly wherein the water quality monitor is made responsive to cyclic operation of the reverse osmosis unit so that accurate and reliable test readings will result. The present invention fulfills these needs and provides further related advantages.